Precision measurement of the mass and lifetime of the ${\Xi }_b^0$ baryon

Abstract

Using a proton-proton collision data sample corresponding to an integrated luminosity of 3 fb${}^{-1}$ collected by LHCb at center-of-mass energies of 7 and 8 TeV, about 3800 ${\Xi }_b^0\to {\Xi }_c^{+}{\pi }^{-}$, ${\Xi }_c^{+}\to p{K}^{-}{\pi }^{+}$ signal decays are reconstructed. From this sample, the first measurement of the ${\Xi }_b^0$ baryon lifetime is made, relative to that of the ${\Lambda }_b^0$ baryon. The mass differences $M({\Xi }_b^0)-M({\Lambda }_b^0)$ and $M({\Xi }_c^{+})-M({\Lambda }_c^{+})$ are also measured with precision more than four times better than the current world averages. The resulting values are $\frac{{\tau }_{{\Xi }_b^0}}{{\tau }_{{\Lambda }_b^0}}=1.006\pm 0.018\pm 0.010$, $M({\Xi }_b^0)-M({\Lambda }_b^0)=172.44\pm 0.39\pm 0.17MeV/c^2$, $M({\Xi }_c^{+})-M({\Lambda }_c^{+})=181.51\pm 0.14\pm 0.10MeV/c^2$, where the first uncertainty is statistical and the second is systematic. The relative rate of ${\Xi }_b^0$ to ${\Lambda }_b^0$ baryon production is measured to be $\frac{f_{{\Xi }_b^0}}{f_{{\Lambda }_b^0}}\frac{\mathcal{B}({\Xi }_b^0\to {\Xi }_c^{+}{\pi }^{-})}{\mathcal{B}({\Lambda }_b^0\to {\Lambda }_c^{+}{\pi }^{-})}\frac{\mathcal{B}({\Xi }_c^{+}\to p{\mathcal{K}}^{-}{\pi }^{+})}{\mathcal{B}({\Lambda }_c^{+}\to p{\mathcal{K}}^{-}{\pi }^{+})}=(1.88\pm 0.04\pm 0.03)\times 10^{-2}$, where the first factor is the ratio of fragmentation fractions, $b\to {\Xi }_b^0$ relative to $b\to {\Lambda }_b^0$. Relative production rates as functions of transverse momentum and pseudorapidity are also presented.

7 pages, 4 figures

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